This invention relates to a power amplifying circuit, such as a final stage amplifier of a radio transmitter, for amplifying an input signal having an electric power in response to an amplification control signal to produce an output signal having an amplified electric power.
The power amplifying circuit is particularly useful in a base station of a mobile radio communication network.
In the mobile radio communication network, a mobile station usually moves in a service area of the base station. A distance between the base station and the mobile station is therefore variable. If the base station transmits a radio signal produced by a usual power amplifying circuit to have a fixed or predetermined electric power, the mobile station receives the radio signal with a variable electric power depending on the distance.
In the manner which will later be described a little more in detail, a conventional power amplifying circuit amplifies the input signal having the electric power in response to an amplification control signal to produce an output signal having an amplified electric power. The control signal controls the amplified electric power so as to keep an electric power of the received radio signal fixed. The conventional power amplifying circuit is defective in that it is impossible to produce the output signal having a desired waveform in a wide range.